What is calcrete? Any good for GOLD PROSPECTING

What is calcrete? Any good for GOLD PROSPECTING.

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Hey guys, Bruce a part-time prospector here. One of the questions I got asked the other day was, what is calcrete and how do I know if it's, I've got it on the ground out in the bush and calcrete is most of us, I think we've ever been out prospecting or even try to dig any type of hole in sort of Outback Australia have encountered calcrete.

Calcrete can occur in multiple forms, but generally it is this white looking rock that seems to either occur in bands, nodules, or as a cement around other types of rocks. It's very, very hard, very hard to dig through and seems to be, in my opinion, feels like it's everywhere, but what is it? calcrete is

calcium carbonate, the same sort of composition that's made up of limestone, but the difference here is limestone occurs at the bottom of the sea from seashells and either bits and pieces of the ocean at the bottom of the ocean. That's where limestone forms, coral reefs, et cetera. Calcrete is a land forming limestone.

In other words, it's a terrestrial limestone terrestrial calcium carbonate deposit. I think it's, its proper, uh, name. And so how does this form, well, just before I start, that most of us see calcrete as a bit of a, basically a pain in the bum. We get a signal in it. We try to hack it out. It's so hard. We end up using a hammer and chisel.

We make a dent in it. We try for a while, and then I've seen too many people just walk away and say. I'll see if I can find another one. OK, so it's generally treated as something to be avoided, but don't! Geologists like to look for calcrete because it can be an amplifier of the gold that's directly below it.

So I'll get to that as we, how they use it by explaining how the calcrete actually forms. So calcrete forms when rainfall falls down, obviously falls down onto the land form. So let me explain this a bit better. Imagine rain soaking into the soil. It picks up tiny bits of calcium and carbon dioxide as it travels.

As the water moves down and evaporates or slows down, it leaves the calcium carbonate behind like mineral rings in a tree to some extent. In dry places, the water gets pulled up through the soil by capillary action like water on sponge or paper towel, lifting the water off the surface.  📍 Imagine rain soaking into the soil. It picks up tiny bits of calcium and carbon dioxide as it travels.

As the water moves down and evaporates or slows down, it leaves the calcium carbonate behind like mineral rings in a tree to some extent. In dry places, the water gets pulled up through the soil by capillary action like water on sponge or paper towel, lifting the water off the surface. Now as it gets near the surface, the water evaporates away and the dissolved calcium carbonate.

Precipitates out and is left behind. This picks up all sorts of stuff in its travels down and up. Even fungi and bacteria have been known to be caught up in, in the , calcrete. Calcrete isn't always one big solid sheet and it comes in lots of different shapes and textures called morphological types.

It could occur as a powdery calc. This is soft and loose and generally occurs further down. Nodular calcrete. Lumpy, bumpy, very, very common. Tubular calc or rassooli is basically tube shaped structures that form around the roots of old plants, and they can look like fossilized tree roots and they can track down through the the soil profile.

Hard pan calcrete is what I was talking about be before, and it seems to be everywhere, is a very hard cemented layer, commonly seen at the bottom of gullies and wash aways, where you can see the calcrete is actually bound together. All the broken rock calcrete is common in dry and semi-dry parts of the world.

I'm not saying just Australia, but parts of the world. It is really widespread in Australia covering about 21% of the land mass. That's higher than most other places in the world, mostly because Australia is more a than most other places in the earth. Apart from Antarctica. It also occurs in the United States.

And over there it is actually called, and I hope I get this right, Calichie. So it's pretty much the same stuff, different name, different place. As I mentioned before, it can help in geologists find gold deposits. So how does this help? Calcrete is a great help in mineral exploration, especially where valuable minerals are deposited deep under lots of regolith.

Basically, you can't sample through the regolith, so it may be windblown sands on top or transported soils You can't sample on top. Elements from the buried deposit can travel up through the ground and get trapped or concentrated in the calcrete layer, which is closer to the surface. Metals dissolve in water, move up and or even tiny bits of minerals can move physically.